Steve S. Doo

Fate of calcifying tropical symbiont-bearing large benthic foraminifera: living sands in a changing ocean.

Concerns regarding the response of calcifiers in future warmer and more acidic oceans have been raised in many studies. Tropical large benthic foraminifera (LBF) are important carbonate producers that reside in coral reefs worldwide. Similar to corals, these organisms live in symbioses with microalgae, which promote high calcification rates. The contribution of LBFs to reef sediments is under threat due to climate change. In this review, we synthesize research conducted on the effects of increased temperature and acidification on these organisms, and assess the potential impacts on reef carbonate production. A meta-analysis of all available experimental data (18 publications, 84 individual experiments) on the effects of ocean warming and acidification on LBF holobiont health was performed using log-transformed response ratios (LnRR) comparing present-day ambient and projected future scenarios. For the latter, we used Representative Concentration Pathway 8.5 from the Intergovernmental Panel on Climate Change, which projects changes of +4 °C and −0.3 pH units by the year 2100. Overall, a general negative trend on holobiont growth was observed across most species of LBFs in response to both stressors. The only exception was the hyaline species (porous CaCO3 test composed of interlocking microcrystals) that have diatom symbionts. Species in this group appear resilient to future ocean acidification scenarios. Differences in the response of LBF species to warming and acidifying oceans may be due to (1) differences in the carbonate species’ use in formation of the CaCO3 skeleton (CO2 vs. CO32-), (2) varied responses of the symbiont types (diatom, dinoflagellate, rhodophyte) to stressors, or (3) the degree of nutritional dependence of the host to its symbiont. We also summarize current estimates of carbonate production by LBFs to provide a context of their contribution to reefs. Finally, we outline major gaps in knowledge in addressing the potential for LBF species persistence in a changing ocean.

3D photogrammetry quantifies growth and external erosion of individual coral colonies and skeletons

Growth and contraction of ecosystem engineers, such as trees, influence ecosystem structure and function. On coral reefs, methods to measure small changes in the structure of microhabitats, driven by growth of coral colonies and contraction of skeletons, are extremely limited. We used 3D reconstructions to quantify changes in the external structure of coral colonies of tabular Acropora spp., the dominant habitat-forming corals in shallow exposed reefs across the Pacific. The volume and surface area of live colonies increased by 21% and 22%, respectively, in 12 months, corresponding to a mean annual linear extension of 5.62 cm yr−1 (±1.81 SE). The volume and surface area of dead skeletons decreased by 52% and 47%, respectively, corresponding to a mean decline in linear extension of −29.56 cm yr−1 (±7.08 SE), which accounted for both erosion and fragmentation of dead colonies. This is the first study to use 3D photogrammetry to assess fine-scale structural changes of entire individual colonies in situ, quantifying coral growth and contraction. The high-resolution of the technique allows for detection of changes on reef structure faster than other non-intrusive approaches. These results improve our capacity to measure the drivers underpinning ecosystem biodiversity, status and trajectory.

Protein Analysis in Large Benthic Foraminifera

Large benthic foraminifera (LBFs) have long been used as environmental recorders of ocean chemistry. Although the importance of foraminifera in paleo-reconstructions of ancient oceans and as sediment producers is well documented, the biology of tropical symbiont-bearing foraminifera has only recently gained increased attention. Tropical symbiont-bearing LBFs represent a unique and important subset of LBFs in that they are vital to coral-reef ecosystems and host a wide suite of algal symbionts (e.g., dinoflagellates, diatoms, red algae, green algae and cyanobacteria). Previous studies on both host and symbiont physiology have been performed in order to gauge the foraminiferal response to a variety of stressors, including elevated temperature and nutrient levels, as well as acidification. Recently, protocols have been developed for protein analysis in LBFs that will allow for expression analyses of target proteins from both members of the holobiont. In this chapter, we detail a protein expression protocol for one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (1-D SDS-PAGE) and consequent western blotting for determination of protein expression in the foraminiferal holobiont. This technique has the potential to target proteins that are specific to either host or symbiont compartments, a breakthrough that may ultimately allow for an increased understanding of the molecular-scale regulation of the symbiosis that is vital to these globally important calcifiers.